Nephrotic syndrome (NS) is a general term that refers to the loss of protein in the urine (proteinuria), hyperlipidemia (hypercholesterolemia and hypertriglyceridemia), and edema. Nephrotic syndrome involves changes in the pathology of cells in the kidney, such as podocytes. Proteinuria is defined as the presence of an excess of serum proteins in the urine. Albuminuria, a specific type of proteinuria, is a pathological condition wherein albumin is present in the urine.
Podocytes (or visceral epithelial cells) are cells in the outer layer of the glomerular capillary loop in the kidneys. The glomerulus filters blood, holding back large molecules such as proteins, and passing through small molecules such as water, salts, and sugar, as the first step in forming urine. The long projections, or “foot processes,” of the podocytes wrap around the capillaries, and come to rest on the glomerular basement membrane. The foot processes are connected by a porous structure called the slit diaphragm. The innermost layer of the glomerular capillary loop is made of fenestrated endothelial cells. Kidneys affected by nephrotic syndrome have abnormalities in the glomerular capillary loop that cause leakage of blood proteins, resulting in proteinuria.
When protein is lost in the urine, its plasma concentration decreases, allowing water to move into other areas of the body, which leads to swelling known as edema. Edema is commonly observed in the feet and legs, in the belly or abdomen (ascites), and around the eyes, but can occur anywhere, especially in response to gravity. Additionally, because of this extra fluid that stays in the body, people often gain weight, experience fatigue and may find that they urinate less often
Many conditions are categorized as nephrotic syndromes, including minimal change disease (MCD), focal segmental glomerulosclerosis (FSGS), membranous nephropathy (MN) (also called membranous glomerulonephritis, MGN), and membranoproliferative glomerulonephritis (MPGN). For years pathologists found no changes in MCD tissue when viewing specimens under light microscopy, hence the name minimal change disease. With the advent of electron microscopy, the changes now known as the hallmarks for the disease include diffuse loss of podocyte foot processes, vacuolation of the podocyte foot processes, and growth of microvilli on the visceral epithelial cells. Diabetic nephropathy is the most common cause of nephrotic syndrome.
Hypertriglyceridemia may occur due to changes in the activity of enzymes that degrade triglycerides, such as lipoprotein lipase (LPL) (2-4). Certain proteins involved in the etiology of nephrotic syndrome and proteinuria, such angiopoietin-like 4 (Angptl4), inhibit the activity of LPL.
The molecular basis of nephrotic syndrome is not known. Increased levels of Angptl4 have been noted in nephrotic syndrome, such as MCD, MN/MGN, and MPGN, but increased circulating levels of Angptl4 have not been associated with causation of proteinuria in nephrotic syndrome. However, the role of Angptl4 in nephrotic syndrome, such as but not limited to, MCD, FSGS, MN/MGN, and MPGN, and related conditions, such as, but not limited to, proteinuria have not been previously reported. Furthermore, the association of proteinuria and glucocorticoid sensitivity in nephrotic syndrome and the link between proteinuria and hypertriglyceridemia, two key components of nephrotic syndrome, have yet to be established. Therapy designed to reduce proteinuria further complicates the study of disease mechanisms. For example, glucocorticoids used to treat proteinuria in MCD independently raise plasma triglyceride levels (5), and normalization of plasma triglyceride levels lags behind the response of proteinuria to glucocorticoids in certain forms of nephrotic syndrome, such as MCD (6).
The present disclosure show that increased circulating levels of Angptl4 reduce the severity of nephrotic syndrome and conditions associated therewith, such as but not limited to, proteinuria. As a result, the present disclosure provides method for treating and/or preventing nephrotic syndrome, such as but not limited to, MCD, FSGS, MN/MGN, MPGN and diabetic nephropathy as well as methods of alleviating symptoms associated with nephrotic syndrome, including, but not limited to, proteinuria and edema. The present disclosure further provides methods for reducing proteinuria and edema.